1. Field of the Invention
The present invention relates to an electrochemical generator apparatus having gaseous oxidant and gaseous hydrocarbon fuel entry means, and containing solid oxide electrochemical cell bundles surrounded and separated by high temperature insulation materials; where the hydrocarbon fuel contacts the surface of materials in the apparatus which are impregnated and/or coated with selected chemicals. The chemical impregnated surfaces are heated in an atmosphere which will form metal oxides or metal oxides plus nickel from the chemicals. The metal oxides prevent degradation which is caused by carbon formation, and, when nickel is included, the combination can also improve the reforming capabilities of the generator.
2. Description of the Prior Art
High temperature solid oxide fuel cells and multi-cell generators have been designed for converting chemical energy into direct current electrical energy, typically in the temperature range of from 700.degree. C. to 1,200.degree. C. Such solid oxide fuel cells, solid oxide fuel cell configurations, and solid oxide fuel cell generators are well known, and taught, for example, by Isenberg in U.S. Pat. Nos. 4,490,444; 4,664,987; and 4,728,584; Makiel in U.S. Pat. No. 4,640,875; and Somers et al., in U.S. Pat. No. 4,374,184.
In all of these applications, the cells in the cell bundles are connected within the insulation cavities and remain exposed to hydrocarbon or other fuels which are fed to contact the fuel electrode. The insulation surrounding the cells provides thermal and electrical insulating functions. The insulation is also placed between cell bundles and around the entire fuel cell assembly. Insulation material can also be fabricated into cell support blocks or boards, fuel distribution boards, and fuel conditioner boards. Insulation used with all of these cell designs is usually porous, low density alumina.
Utilization of both methane, and natural gas containing higher hydrocarbons as fuels is possible in the generator. In all the prior art designs, however, during long term operation on hydrocarbon fuels, there is a possibility of some performance degradation and electrical shorting between cell bundles through separating insulation and cell support blocks due to carbon deposition, especially when higher hydrocarbons are used in the fuel. Also, in some instances, during long term cell operation, fuel entry tubes, passages, and distribution boards may start to clog up due to carbon formation, and the main insulation itself, surrounding the entire cell assembly, i.e., next to the generator walls, can become coated and surrounded with encapsulating carbon, with some loss of insulation effect. Carbon formed on the fuel distribution board on which the cells rest, can also result in some loss of performance.
Carbon deposition on most of these surfaces is thought to result from lack of water adsorption on the surfaces, leading to minimal gasification of carbon from adsorbed hydrocarbons. If H.sub.2 O is not present on the surface, the oxygen species necessary to react with adsorbed carbon species, to form CO and CO.sub.2 gases, will not be present in sufficient quantity, and hence will result in formation of carbon which is encapsulating in nature and remains resistant to oxidation by the H.sub.2 O present in the gaseous fuel atmosphere. Removal of such carbon, once formed, is usually difficult.
In the area of catalytic reforming of heavy gaseous and/or liquid hydrocarbons containing sulfur, utilizing the injection of steam to produce hydrogen, but not involving fuel cells, Setzer et al., in U.S. Pat. No. 4,451,578, teaches high activity iron oxide catalysts which demonstrate a better resistance to carbon plugging than nickel catalysts. The catalyst can be unsupported and contain 90% FeO or Fe.sub.2 O.sub.3 plus modifiers such as Al.sub.2 O.sub.3, K.sub.2 O, CaO or SiO.sub.2, or the catalyst can be unmodified, and supported on Al.sub.2 O.sub.3, CaO impregnated Al.sub.2 O.sub.3 and La stabilized Al.sub.2 O.sub.3 . In a typical example, 0.318 cm (0.125 inch) diameter Al.sub.2 O.sub.3 pellets were impregnated with Ca(NO.sub.3).sub.2, placed in an ultrasonic blender, dried, and then calcined at 1,010.degree. C. This material was then impregnated with Fe(NO.sub.3).sub.3 .multidot.H.sub.2 O, dried, and then calcined at 1,000.degree. C.
Carbon deposition on metal conduits or metal chambers containing Ni, Fe, and Co, utilized in hydrocarbon thermal cracking apparatus, was recognized by Watanabe et al., in U.S. Pat. No. 4,692,313. In this patent, thermal cracking is used to provide smaller hydrocarbon fractions. The cracked hydrocarbons are not eliminated. There, a carbon formation inhibitor element, selected from Li, Na, K, Ba, Be, Ca, Mg, or their oxides, is incorporated directly into the metal alloy of the conduit or chamber. Alternatively, a carbon deposition suppressing inner layer, containing a Li, Na, K, Ba, Be, Ca, or Mg inhibitor element, or their oxides, usually with chromium alloy, is cast or plasma sprayed onto the inner surface of the metal conduit or metal chamber. The usual ratio of chromium alloy inhibitor element or their oxides, in the inner layer, is about 10:1.
What is needed, for electrochemical generators using a gaseous hydrocarbon fuel and operating at 700.degree. C. to 1,200.degree. C., is a means to prevent carbon formation on separating insulation partitions for cell bundles, cell support blocks, main generator insulation, fuel conditioner boards, and fuel entry tubes, passages and distribution boards. The main object of this invention to provide such a means.